1. Field of the Invention
The present invention relates to an exposure apparatus and a device manufacturing method.
2. Description of the Related Art
A technique used for securing a plane to another plane by fixing three places is discussed in Japanese Patent Application Laid-Open No. 08-114250. Three places are fixed in securing a plane since fixing four or more places will cause excessive constraint which leads to a bending stress in the plane. Japanese Patent Application Laid-Open No. 2001-44264 discusses an exposure apparatus including a structure for supporting a reticle stage which is supported at three places on a mount. Further, as illustrated in FIGS. 9 and 10, an exposure apparatus is known which includes a structure 504 supported at three places on a structure 502. The support is provided by three supporting members 503, two of which are visible in FIG. 9. The structure 504 is configured to support a reticle stage 505 and the structure 502 is configured to support a projection optical system 501.
As illustrated in FIG. 10, a shape of the structure 504 for supporting the reticle stage 505 is generally rectangular. Thus, according to the exposure apparatus in which three supporting members 503 are arranged as illustrated in FIGS. 9 and 10, two of the four corner portions of the structure 504 for supporting the reticle stage 505 will be distant from the supporting members 503. Amplitude of vibration at the corner portions which are not supported by the supporting members 503 increases compared to the corner portions which are supported by the supporting members 503 because the unsupported portions are arranged in a cantilever fashion. Vibration at the corner portions which are not supported is caused by a movement of the reticle stage 505 as well as vibration transmitted from the floor or a wafer stage. Vibration of a mirror or a measurement reference device (not shown) such as an interferometer which is set on the structure 502 for supporting the projection optical system 501 causes an error in a position measurement of the stage. This results in poor alignment at the time of exposure.
Such vibration is more significant when the apparatus is heavier. Thus, the effect of the vibration is more significant as for a heavier reticle stage or a heavier structure which supports the reticle stage than for lighter ones.